The overall goal of this project is to define the molecular mechanisms associated with alterations in the respiratory control system caused by intermittent hypoxia (IH). The studies in the current proposal will examine the importance of hypoxia-inducible transcription factor (HIF-1) in these alterations. This proposal is based on our recent findings that: a) 10 days of IH enhances the hypoxic ventilatory response (HVR) in wild type (Wt) but not in mice deficient in HIF-1 alpha, the regulatory subunit of HIF-1 complex; b) IH increases Hypoxic-Responsive Element (HRE)-reporter gene activity in cell cultures, suggesting that IH activates HIF-1; and c) an equivalent duration and intensity of sustained hypoxia (SH) has no effect on HRE-reporter gene activity, suggesting that IH is more potent than SH in activating HIF-1. There is considerable data suggesting that IH enhances the response of the respiratory control system to hypoxia, which in turn leads to hypertension. Given that IH occurs more often in life than SH, and IH is associated with many pathophysiological conditions, it is of great importance to understand the molecular mechanisms associated with IH. The current proposal tests two primary hypotheses: 1) HIF-1 transcription factor plays an essential role in the increased ventilatory chemosensitivity to hypoxia caused by IH; and 2) reactive oxygen species (ROS) and Calcium2+-signaling pathways are involved in IH-induced activation of HIF-1. We propose to test these hypotheses using two experimental strategies; one involving intact mice deficient in HIF-1 alpha (+/-), and another involving cell cultures. Aim 1 will examine the role of HIF-1 in the IH-induced increase in the ventilatory response to hypoxia. Aim 2 will determine the importance of HIF-1 in long-term effects of IH on dynamic properties of the respiratory control system that include short term potentiation, short-term depression, long-term facilitation, and hypoxic ventilatory decline. Aim 3 will assess the mechanisms by which IH activates HIF-1. Lastly, Aim 4 seeks to identify the down stream genes affected by IH in respiratory related structures. We will employ the GeneChip hybridization technology that allows simultaneous assessment of relative mRNA expression levels of a broad array of genes including genes for neurotransmitters, ion channels and energy metabolism. Genes activated by IH will be compared in Wt and HIF-1 alpha (+/-) mice. This project is thematically related to the overall theme of the Program Project Grant because it examines the potential role of HIF-1 transcription factor in the ventilatory changes in response to IH. This project is also thematically related to Projects 17, 18, 14, 19 and 20. Aims 2 and 4 will be conducted in collaboration with Dr. Dick, Dr. Kunze and Dr. Kumar.